Where has the "Show in Viewport" option in the 2.8 branch of Animation-Nodes gone?
This option has been replaced by a more advanced node called the Viweport Input node. Every Viweport Input node creates an input box in the AN panel, the name of the input box is defined by the label of the Viweport Input node that defines it. The boxes can be minimized and you can change the order of inputs as you wish from the N menu. For instance, we have here two Viweport Input nodes defining two input boxes: